Clean up

advanced_knowledge/merkle_trees/README.md

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+## a place to dump merkle trees examples
+
+<br>
+
+* disclaimer: these boilerplates might not be my code, but rather well-known references.

advanced_knowledge/merkle_trees/tree_example1.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.17;
+
+// Merkle tree allows you to cryptographically prove that an element is contained
+// in a set without revealing the entire set.
+
+contract MerkleProof {
+    function verify(
+        bytes32[] memory proof,
+        bytes32 root,
+        bytes32 leaf,
+        uint index
+    ) public pure returns (bool) {
+        bytes32 hash = leaf;
+
+        for (uint i = 0; i < proof.length; i++) {
+            bytes32 proofElement = proof[i];
+
+            if (index % 2 == 0) {
+                hash = keccak256(abi.encodePacked(hash, proofElement));
+            } else {
+                hash = keccak256(abi.encodePacked(proofElement, hash));
+            }
+
+            index = index / 2;
+        }
+
+        return hash == root;
+    }
+}
+
+contract TestMerkleProof is MerkleProof {
+    bytes32[] public hashes;
+
+    constructor() {
+        string[4] memory transactions = [
+            "alice -> bob",
+            "bob -> dave",
+            "carol -> alice",
+            "dave -> bob"
+        ];
+
+        for (uint i = 0; i < transactions.length; i++) {
+            hashes.push(keccak256(abi.encodePacked(transactions[i])));
+        }
+
+        uint n = transactions.length;
+        uint offset = 0;
+
+        while (n > 0) {
+            for (uint i = 0; i < n - 1; i += 2) {
+                hashes.push(
+                    keccak256(
+                        abi.encodePacked(hashes[offset + i], hashes[offset + i + 1])
+                    )
+                );
+            }
+            offset += n;
+            n = n / 2;
+        }
+    }
+
+    function getRoot() public view returns (bytes32) {
+        return hashes[hashes.length - 1];
+    }
+
+    /* verify
+    3rd leaf
+    0xdca3326ad7e8121bf9cf9c12333e6b2271abe823ec9edfe42f813b1e768fa57b
+
+    root
+    0xcc086fcc038189b4641db2cc4f1de3bb132aefbd65d510d817591550937818c7
+
+    index
+    2
+
+    proof
+    0x8da9e1c820f9dbd1589fd6585872bc1063588625729e7ab0797cfc63a00bd950
+    0x995788ffc103b987ad50f5e5707fd094419eb12d9552cc423bd0cd86a3861433
+    */
+}